book3s64/hash: Refactor hash__kernel_map_pages() function

This refactors hash__kernel_map_pages() function to call
hash_debug_pagealloc_map_pages(). This will come useful when we will add
kfence support.

No functionality changes in this patch.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/0cb8ddcccdcf61ea06ab4d92aacd770c16cc0f2c.1729271995.git.ritesh.list@gmail.com